Add an option to build libFuzzer from DEPS.

The bots will need to get libFuzzer externally. As usual, borrow
Chromium's copy.

Change-Id: I5ed879bbc76188838adcf9d51855e76c481ace5b
Reviewed-on: https://boringssl-review.googlesource.com/16146
Reviewed-by: Steven Valdez <svaldez@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
diff --git a/.gitignore b/.gitignore
index 9f396f6..41c6e96 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,6 +14,7 @@
 util/bot/cmake-win32.zip
 util/bot/golang
 util/bot/gyp
+util/bot/libFuzzer
 util/bot/llvm-build
 util/bot/perl-win32
 util/bot/perl-win32.zip